Complex ester base lubricating grease compositions



COMPLEX ESTER BASE LUBRICATING GREASE CONIPOSITIONS David W. Young, Westfield, Arnold J. Morway, Clark Township, Union County, and Delmer L. Cottle, Highland Park, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application July 5, 1952, Serial No. 297,386

6 Claims. (Cl. 252-42) This invention relates to lubricating grease compositions. Particularly the invention relates to lubricating greases having outstanding low temperature properties which utilize as the dispersing agent a complex ester synthetic lubricant prepared from a branched chain alcohol, a dibasic acid and a 1,3-glycol.

It is known in the lubricating art that the dispersing agent most desirable for a grease formulation is the lubricating oil which would be selected for the lubricating application if a lubricating oil could be used. That is to say, when the application of the lubricant calls for a lubricating grease composition, the best grease is one which is made from a lubricating oil which would furnish the best lubrication if a liquid could be used. This premise is basic in the art of lubricating grease manufacture.

In lubrication applications that call for an outstanding lubricant particularly in respect to wide temperature ranges, it has been found that synthetic lubricants are generally more satisfactory than mineral base lubricants. This is particularly true in the lubrication of moving parts of jet engines used in aircraft, either the turbo-jet engine or the turbo-prop. Extremely varied temperature range is experienced by these engines and it has been found in the past that mineral oil based lubricants are generally unsatisfactory. Accordingly, the lubricating art has developed a line of synthetic lubricants for these applications.

Some of the most popular of these synthetic lubricants are those of the ester type. Synthetic lubricating oils which comprise. esters of dibasic acids and complex esters formed from mixtures of alcohols, dibasic acids and gly-cols have been found to be of outstanding importance in meeting the stringent conditions imposed upon lubricants by this modern technology. It is with the complex ester type of the synthetic lubricants that this invention is concerned.

One of the major problems in the manufacture of the complex ester synthetic lubricant has been the high residual acidity of the final product. This high residual acidity is harmful in that the corrosivity to contacting metal parts at high temperatures causes a rapid deterioration of the bearing surfaces. Therefore the application of these otherwise excellent complex ester type synthetic oils has been curtailed.

A complex ester type synthetic oil having outstanding low temperature properties may be prepared by the interaction of 2 molecular proportions of a branched chain alcohol having from 6 to 16 carbon atoms, such as branched hexanols, heptanols, octanols, 6 methyl lheptanol, 2 n-propyl-l-pentanol, 3 n-propyl-l-pentanol,2,2- dimethyl-l-octanol, 4,5-dimethyl hexanol, 3,5-dimethyl hexanol, di-2-ethylhexanol, Cs Oxo alcohol, C9 Oxo alcohol, C13 Oxo alcohol, etc. with 2 molecular proportions of a dibasic acid, such as adipic, azelaic, sebacic or glutaric acid, and with 1 molecular proportion of a 1,3-glycol. The preparation of one such synthetic lubricating oil is set out in detail as follows:

nitecl States Patent Cficc Patented June 19, 1956 180 grams (2 mols) of a glycol, e. g. butane diol 1,3, 520 grams (4 mols) of a branched chain alcohol having 8 carbon atoms, e. g. Ca 0x0 or isooctyl alcohol, 584 grams (4 mols) of adipic acid, 6.4 grams of 2,6 dit-butyl-4-methyl phenol and 200 grams of xylene were placed in a 2 liter 3-neck flask fitted with a water cooled condenser and a side arm takeoff tube, used to remove the water of reaction. The mixture was heated at the boiling point for 16 hours and at this point 138 ml. of water as a by-product was removed. However, the ester has an acid number equal to 66.8 ml. KOH (0. 1 N) per 5 ml. of sample. To help reduce the acidity 45 grams more of 1,3-butane diol was added and the mixture heated for 16 more hours at the boiling point. At this point the acidity was 10.3 ml. of KOH (0.1 N) per 5 ml. of sample. As this acid number was still quite high there was added 22.5 grams more of 1,3-butane diol and 65.0 grams of isooctyl alcohol. Upon heating to the boiling point for 16 more hours the acidity was reduced to 0.5 ml. of KOH (0.1 N) per 5 ml. sample. The sample at this point was heated under 3 mm. Hg vacuum to a pottemperature of 200 C. and an overhead temperature of 143 C. The total weight of final ester as bottoms after stripping was 1313 grams and the by-product overhead was 254 grams.

This complex ester had the following ASTM inspections:

Pour point (F.) Viscosity at 210 F. (cs.) 5.35 Viscosity at F. (CS.). J 26.15 Viscosity at -40 F. (cs.) 9997.0 Flash point F.) 440 Acid No. (ml.) KOH/5 g. sample .5

This ester has excellent low temperature properties as evidenced by the viscosity at -40 F. It also has outstanding viscosity-temperature relationship as is shown by the viscosity at 100 F. and 210 F. Its flash point is suificiently high so as to make it applicable for lubrication at extremely high temperatures. However, it will be noted that the acid number of the ester indicates that its residual acidity makes it undesirable for lubricating use in some applications.

As was stated above the use of this synthetic ester lubricant as a dispersing agent for greasecompositions would be desirable in applications where its low temperature and good viscosity-temperature relationships could be utilized. However, its high residual acidity again would militate against its choice. It has now been found and forms the object of this invention that a grease composition using this complex ester may be prepared by a process whereby its residual acidity is removed. The resulting grease composition contains no harmful residual acidity and retains all the desirable properties of the complex ester.

It has been found in the lubricating grease art that attempts to prepare a lubricating grease utilizing a synthetic oil by ordinary grease forming techniques are unsuccessful. This is due to the fact when common soap forming acids are utilized with a metal base such as a metallic hydroxide, hydrolyzation of the ester occurs and the resulting product is a mixture of soap and the various components of the ester. According to the instant invention however the soap thickener is prepared ina mineral lubricating oil in such a manner that an excessof the metallic hydroxide is present. This excess metallic hydroxide then neutralizes the residual acidity of the.

the formulation of the lubricating greases of this invention is as follows:

EXAMPLE I Formulation Percent Hydrogenated fish oil acid Lithium hydroxide monohydrate 2.20 Phenothiazine 0.5 Mineral oil (35 SUS at 210 F.) Complex ester described above 62.3

Procedure The hydrogenated substantially saturated fish oil acids (Hydrofol 54) and the mineral oil were charged to a fire heated grease kettle equipped with efficient means of agitation and heated to 150 F. The lithium hydroxide monohydrate was then charged as a hot 15% aqueous solution. Heating was continued to 250-300 P. where the soap was completely dry. The complex ester was then added and the temperature raised to 420 F. The phenothiazinc was added and the fluid material drawn into pans in thin layers where it was rapidly cooled. The cold cakes of grease were then returned to a cold kettle, worked to a homogeneous mass, and milled or homogenized to a uniform product.

Resulting grease composition had the following ASTM inspections:

Penetration (mm./ 10, 77 F.):

Unworked 295. Worked (60 strokes) 320. Water solubility Insoluble in boiling water. Percent free alkalinity- 0.05 (as LiOH).

This grease formulation was submitted to NLGI-ABEC spindle life test which is described in detail in the December 1949 addition to Lubrication, vol. 35, No. 12, a technical publication devoted to the selection and use of lubricants, published by the Texas Oil Company. Operating at 250 F. at 10,000 R. P. M. this grease gave a spindle life of 1400 hours.

In the standard Norma-Hoffman oxidation bomb test, the grease of Example I gave the following results, indicating excellent resistance to oxidation:

P. s. i. drop in The hydroxy stearic acid was charged along with the diester to a fire heated grease kettle and warmed to 150 F. A 15% hot aqueous solution of the lithium monohydrate was added and the soap dehydrated at 250300 F. The complex ester was charged and the grease heated to 420 F. The phenothiazine was added and incorporated and the molten grease drawn into pans in shallow layers for cooling. The cold grease was returned to the cold kettle, worked down to desired penetration, milled, filtered, and packaged.

This grease composition was a, smooth excellent appearing product which gave the following ASTM inspections:

Penetration (mm./10, 77 F.):

This grease composition was submitted to the standard Norma-Hoffman oxidation bomb test and gave only a 5 p. s. i. drop in pressure at the end of 210 hours, indicating excellent oxidation resistance.

To summarize briefly this invention relates to lubricating grease compositions utilizing as a base oil a synthetic ester lubricant which has outstanding low temperature properties and excellent oxidation resistance characteristics. This synthetic lubricating oil base is of the complex ester type and is prepared by reaction between a branched chain alcohol having from 6 to 10 carbon atoms, a dibasic acid such as adipic, sebacic, glutaric and the like and a l-3 glycol representative of which is 1-3 butane diol. The synthetic lubricating oil base is thickened to a grease consistency with from 2% to 20% by weight based on the weight of the total composition and preferably from 2.5% to 10% by weight of the lithium soap of a high molecular weight substantially saturated fatty acid such as hydrogenated fish oil acid. The synthetic lubricating oil used as a base in the preferred embodiment of this invention has a residual acidity which makes it impractical for use as a lubricating oil, thus the undesirable characteristic is removed in the grease formulation of the invention by utilizing a lithium soap that is alkaline. The resulting grease composition is neutral or slightly on the alkaline side. These novel lubricating grease compositions are prepared by first dispersing the lithium soap in a mineral oil using about 20% to 60% by weight of said oil based on the weight of the total formulation. After heating the mixture of oil and soap to disperse the soap the synthetic lubricating oil base is blended into the composition. The mixture is heated to dehydrate the soap and the resulting composition is cooled and the grease structure is formed.

In the preparation of the complex ester synthetic oils used in the present invention various combinations of alcohols may be used as well as single alcohols of branched chain structure having from 6 to 18 carbon atoms per molecule. In general the alcohols are saturated and of branched chain. The preferred dibasic acids are adipic, azelaic, succinic and glutaric, though other saturated acids of this series, C4 to C10, can be used. The glycols are preferably the 1,3-glycols such as 1,3- butane diol, methyl butane diol 1,3, and pentane diol 1,3. Although lithium soaps are preferred as thickening agents, other metal soaps such as those of sodium, potassium, calcium, barium, strontium and aluminum may be used as part or all of the thickener. Hence the hydroxides of these metals may be used with or in lieu of lithium hydroxide in some cases. The use of other and conventional modifiers such as antioxidants, corrosion inhibitors, tackiness agents, extreme pressure additives, etc., in conventional quantities is contemplated also as will be obvious to those skilled in the art.

What is claimed is:

l. A lubricating grease composition which comprises a complex ester synthetic lubricating oil formed from two mols of a branched C6 to C16 alcohol, two mols of a C4 to C10 dibasic acid and one mol of a 1-3 glycol selected from the group consisting of butanediol-l,3, methyl butanediol-1,3 and pentanediol-1,3, said oil being thickened to a grease consistency with the lithium soap of hydrogenated fish oil acid.

2. A lubricating grease composition which comprises a complex ester synthetic lubricating oil formed by esterifying one mol of a 1-3 glycol selected from the group consisting of butanediol-1,3, methyl butanediol-l,3 and pentanediol-l,3 with two mols of a C4 to C dibasic acid and two mols of a C6 to C12 branched chain alcohol, said oil being thickened to a grease consistency with from 2% by Weight to by weight, based on the total composition, of the lithium soap of hydrogenated fish oil acid.

3. A lubricating grease composition which comprises a complex ester synthetic lubricating oil formed by esterifying one mol of a 1-3 butane diol with two mols of isooctyl alcohol and two mols of adipic acid, said oil being thickened to a grease consistency with from 2.5% to 10% by weight, based on the total composition, of the lithium soap of hydrogenated fish oil acids.

4. A process for the preparation of lubricating grease compositions which comprise the steps of dispersing in a minor amount of a mineral lubricating oil base stock from 2% to 20% by weight, based on the total ultimate composition, of the lithium soap of hydrogenated fish oil acid which contains an excess of lithium hydorxide, heating the mixture to completely melt said soap, adding to the dispersed mixture from 40% to 80% by weight of a synthetic lubricating oil of the complex ester formed from a C6 to C16 branched chain alcohol, a C4 to C10 dibasic acid and a 1-3 glycol selected from the group consisting of butanediol-1,3, methyl butanediol-1,3 and pentanediol-1,3, further heating the resulting mixture to dehydrate said soap and cooilng to obtain a finished grease composition.

5. A process according to claim 4 wherein said synthetic lubricating oil is formed by reacting two mols of isooctyl alcohol and two mols of adipic acid with one mol of 1-3 butane diol and wherein said lithium soap is used in amounts between about 2.5% and 10% by weight based on the weight of the total composition.

6. A process for the preparation of lubricating grease compositions which comprise the steps of dispersing in a minor amount of a mineral lubricating oil base stock from 2% to 20% by weight, based on the total ultimate composition, of lithium soap of hydrogenated fish oil acid which contains an excess of the hydroxide of said metal, heating the mixture to completely melt said soap, adding to the dispersed mixture from to by weight of a synthetic lubricating oil of the complex ester formed from a C6 to C16 branched chain alcohol, a C4 to C10 dibasic acid and a 1-3 glycol selected from the group consisting of butanediol-1,3, methyl butanediol-l,3 and pentanediol-L3, further heating the resulting mixture to dehydrate said soap and cooling to obtain a finished grease composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,173 Brunstrum Apr. 9, 1946 2,436,347 Zimmer et a1. Feb. 17, 1948 2,575,195 Smith Nov. 13, 1951 2,628,974 Sanderson Feb. 17, 1953 2,639,266 Dilworth et a1. May 19, 1953 2,652,361 Woods et a1. Sept. 15, 1953 

2. A LUBRICATING GREASE COMPOSITION WHICH COMPRISES A COMPLEX ESTER SYNTHETIC LUBRICATING OIL FORMED BY ESTERIFYING ONE MOL OF A 1-3 GLYCOL SELECTED FROM THE GROUP CONSISTING OF BUTANEDIOL-1,3, METHYL BUTANEDIOL-1,3 AND PENTANEDIOL-1,3 WITH TWO MOLS OF A C4 TO C10 DIBASIC ACID AND TWO MOLS OF A C8 TO C12 BRANCHED CHAIN ALCOHOL, SAID OIL BEING THICKENED TO A GREASE CONSITENCY WITH FROM 2% BY WEIGHT TO 20% BY WEIGHT, BASED ON THE TOTAL COMPOSITION, OF THE LITHIUM SOAP OF HYDROGENATED FISH OIL ACID. 